1. Field of the Invention
This invention relates to an electron beam apparatus and also to an image-forming apparatus such as display apparatus that can be realized by using it.
2. Related Background Art
There have been known two types of electron-emitting device; the hot cathode type and the cold cathode type. Of these, the cold cathode type refers to devices including surface conduction electron-emitting devices, field emission type (hereinafter referred to as the FE type) devices and metal/insulation layer/metal type (hereinafter referred to as the MIM type) electron-emitting devices.
Examples of surface conduction electron-emitting device include one proposed by M. I. Elinson, Radio Eng. Electron Phys., 10, 1290, (1965) as well as those that will be described hereinafter.
A surface conduction electron-emitting device is realized by utilizing the phenomenon that electrons are emitted out of a small thin film formed on a substrate when an electric current is forced to flow in parallel the film surface. While Elinson proposes the use of SnO2 thin film for a device of this type, the use of Au thin film is proposed in [G. Dittmer: “Thin Solid Films”, 9, 317 (1972)] whereas the use of In2O3/SnO2 and that of carbon thin film are discussed respectively in [M. Hartwell and C. G. Fonstad: “IEEE Trans. ED Conf.”, 519 (1975)] and [H. Araki et al.: “Vacuum”, Vol. 26, No. 1, p. 22 (1983)].
FIG. 19 of the accompanying drawings schematically illustrates a typical surface conduction electron-emitting device proposed by M. Hartwell. In FIG. 19, reference numeral 3001 denotes a substrate. Reference numeral 3004 denotes an electroconductive thin film normally prepared by producing an H-shaped thin metal oxide film by means of sputtering, part of which eventually makes an electron-emitting region 3005 when it is subjected to an electrically energizing process referred to as “energization forming” as will be described hereinafter. In FIG. 19, the thin horizontal area of the metal oxide film separating a pair of device electrodes has a length L of 0.5 to 1 [mm] and a width W of 0.1 [mm]. Note that, while the electron-emitting region 3005 has a rectangular form and is located at the middle of the electroconductive thin film 3004, there is no way to accurately know its location and contour.
For preparing surface conduction electron-emitting devices including those proposed by M. Hartwell et al., the electroconductive film 3004 is normally subjected to an electrically energizing process, which is referred to as “energization forming”, to produce an electron-emitting region 3005. In the energization forming process, a constant DC voltage or a slowly rising DC voltage that rises typically at a rate of 1V/min. is applied to given opposite ends of the electroconductive film 3004 to partly destroy, deform or transform the thin film and produce an electron-emitting region 3005 which is electrically highly resistive. Thus, the electron-emitting region 3005 is part of the electroconductive film 3004 that typically contains a gap or gaps therein so that electrons may be emitted from the gap. Note that, once subjected to an energization forming process, a surface conduction electron-emitting device comes to emit electrons from its electron emitting-region 3005 whenever an appropriate voltage is applied to the electroconductive film 3004 to make an electric current run through the device.
Examples of FE type device include those proposed by W. P. Dyke & W. W. Dolan, “Field emission”, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, “Physical Properties of thin-film field emission cathodes with molybdenum cones”, J. Appl. Phys., 47, 5248 (1976).
FIG. 20 of the accompanying drawings illustrates in cross section a typical FE type device. Referring to FIG. 20, the device comprises a substrate 3010, an emitter wiring 3011, an emitter cone 3012, an insulation layer 3013 and a gate electrode 3014. When an appropriate voltage is applied between the emitter cone 3012 and the gate electrode 3014 of the device, the phenomenon of field emission appears at the top of the emitter cone 3012.
Apart from the multilayer structure of FIG. 20, an FE type device may also be realized by arranging an emitter and a gate electrode on a substrate substantially in parallel with the substrate.
MIM devices are disclosed in papers including C. A. Mead, “Operation of tunnel-emission Devices”, J. Appl. Phys., 32,646 (1961). FIG. 21 illustrates a typical MIM device in cross section. Referring to FIG. 21, the device comprises a substrate 3020, a lower metal electrode 3021, a thin insulation layer 3022 as thin as 100 angstroms and an upper electrode having a thickness between 80 and 300 angstroms. Electrons are emitted from the surface of the upper electrode 3023 when an appropriate voltage is applied between the upper electrode 3023 and the lower electrode 3021 of the MIM device.
Cold cathode devices as described above do not require any heating arrangement because, unlike hot cathode devices, they can emit electrons at low temperature. Hence, the cold cathode device is structurally by far simpler than the hot cathode device and can be made very small. If a large number of cold cathode devices are densely arranged on a substrate, the substrate is free from problems such as melting by heat. Additionally, while the hot cathode device takes a rather long response time because it operates only when heated by a heater, the cold cathode device starts operating very quickly. Therefore, studies have been and are currently being conducted on cold cathode devices.
For example, since a surface conduction electron-emitting device has a particularly simple structure and can be manufactured in a simple manner, a large number of such devices can advantageously be arranged on a large area without difficulty. As a matter of fact, a number of studies have been made to fully exploit this advantage of surface conduction electron-emitting devices. Studies that have been made to arrange a large number of devices and drive them effectively include the one described in Japanese Patent Application Laid-Open No. 64-31332 filed by the applicant of the present patent application.
Applications of surface conduction electron-emitting devices that are currently being studied include charged electron beam sources and electron beam apparatuses such as image displays and image recorders.
U.S. Pat. No. 5,066,883, Japanese Patent Application Laid-Open Nos. 2-257551 and 4-28137 also filed by the applicant of the present patent application disclose image display apparatuses realized by combining surface conduction electron-emitting devices and a fluorescent panel that emits light as it is irradiated with electron beams. An image display apparatus comprising surface conduction electron-emitting devices and a fluorescent panel can be highly advantageous relative to comparable conventional apparatuses such as liquid crystal image display apparatuses that have been popular in recent years because it is of a light emissive type and does not require a backlight to make it glow.
On the other hand, U.S. Pat. No. 4,904,895 of the applicant of the present patent application discloses an image display apparatuses realized by arranging a large number of FE-type devices. Other examples of image display apparatus comprising FE-type devices include the one reported by R. Meyer [R. Meyer: “Recent Development on Microtips Display at LETI”, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, p.p 6-9 (1991)].
Japanese Patent Application Laid-Open No. 3-55738 also filed by the applicant of the present patent application describes an image display apparatus realized by arranging a large number of MIM-type devices.
Of the known image-forming apparatus comprising electron-emitting devices, those of a flat type are attracting attention and expected to replace display apparatus of the cathode ray tube type because they take little space and lightweight.
FIG. 22 is a schematic perspective view of a flat type image-forming apparatus, showing the inside by partly cutting away the display panel.
Referring to FIG. 22, there are shown a rear plate 3115, lateral walls 3116 and a face plate 3117. The envelope (airtight container) of the image-forming apparatus for maintaining the inside of the display panel in a vacuum state is formed by the rear plate 3115, the lateral walls 3116 and the face plate 3117.
A substrate 3111 is rigidly secured to the rear plate 3115 and a total of N×M cold cathode devices 3112 are arranged on the substrate 3111 (where N and M represents natural numbers not smaller than 2 that may or may not be different from each other and will be selected appropriately depending on the number of pixels to be used for displaying an image). As shown in FIG. 22, the N×M cold cathode devices are wired by M row directional wires 3113 and N column directional wires 3114. The unit comprised of the substrate 3111, the cold cathode devices 3112, the row directional wires 3113 and the column directional wires 3114 is referred to as multi-electron beam source. An insulation layer (not shown) is arranged for electric insulation between the row directional wires 3113 and the column directional wires 3114 at least at the crossings of the row directional wires 3113 and the column directional wires 3114.
A fluorescent film 3118 comprising fluorescent bodies (not shown) of the three primary colors of red (R), green (G) and blue (B) is arranged on the lower surface of the face plate 3117. Black members (not shown) are arranged to isolate each of the fluorescent bodies of the fluorescent film 3118 and a metal back 3119 typically made of Al is arranged on the side of the fluorescent film 3118 facing the rear plate 3115.
In FIG. 22, Dx1 through Dxm, Dy1 through Dyn and Hv represents respective electric terminals provided to electrically connect the display panel and an electric current (not shown) and having an airtight structure. The terminals Dx1 through Dxm are electrically connected to the row directional wires 3113 of the multi-electron beam source and the terminals Dy1 through Dyn are electrically connected to the column directional wires 3114 of the multi-electron beam source, whereas the terminal Hv is electrically connected to the metal back 3119.
The inside of the airtight container is held to a degree of vacuum of about 10−6 Torr. As the display area of the image-forming apparatus increases, means will have to be provided to prevent the rear plate 3115 and the face plate 3117 against deformation and/or destruction due to the pressure difference between the inside and the outside of the air tight container. The use of a thick rear plate 3115 and a thick face plate 3116 is not feasible because it can increase the weight of the image-forming apparatus and the image displayed on the display panel can become distorted or be accompanied by a phenomenon of parallax if viewed askant. Thus, structural supports (that are referred to as spacers or ribs) 3120 that are made of a thin glass plate are arranged in the airtight container of FIG. 22 in order to make the rear plate 3115 and the face plate 3116 withstand the atmospheric pressure. The substrate 3111 carrying thereon a multi-electron beam source and the face plate 3116 carrying thereon a fluorescent film 3118 are then separated by a distance between a fraction of a millimeter and several millimeters and the inside of the airtight container is held to an enhanced degree of vacuum as described earlier.
As a voltage is applied to the cold cathode devices 3112 of an image-forming apparatus comprising a display panel as described above by way of the extra-container terminals Dx1 through Dxm and Dy1 through Dyn, each of the cold cathode devices emits electrons. Then, a high voltage between several hundred volts and several kilovolts is applied to the metal back 3119 by way of the extra-container terminal Hv to accelerate the emitted electrons and make them collide with the inner surface of the face plate 3117. As a result of this, the fluorescent bodies of the three primary colors of the fluorescent film 3118 are energized to emit light and display an image on the display panel.